In computer graphics, it is often necessary to render (e.g., shade) an irregularly shaped surface—that is, a surface that is not a regular geometric shape, or that has edges that curve in different directions and/or have different radii of curvature. Various techniques may be used to render such surfaces. In some of these techniques, a per-pixel mask representative of the surface is generated. For example, pixels that are covered by the surface are designated as such by setting a bit per pixel, while the bit is not set for pixels that are not covered by the surface.